Magnesium alloy and method of treatment



Patented Sept. 2 1 952 it;

ltIAGNESIUM ALLYOYYAND METHonpE,

- TREATMENT 'Jerzy Wr'Meier, Ottawa, Ontario; Canada, 'as- Signor to HerMajesty the Queen in the right of Canada -a s represented by theMinister. off Mines andlTe'chhical Surveys 7 1 l No Drawing.-App1ication January 22,1949, S.e-

rial'No:T72,2 60 ..'Jlnicanadaioctober-7,1948.. e. I. r. I

This invention relates to magnesium casting alloys and a method oftreating the same and more particularly to a magnesium casting alloycontaining both zinc and zirconium.

Zirconium has been classified among metals which have the capacity toharden alloys. It is known to have the property of reducing thegrain-size of magnesium alloys. Zinc has been used in magnesium alloys.

The object of the present invention is to provide an alloy which has amaximum ratio of strength to weight in order to best adapt it for use inairborne and transportation equipment where weight is a majorconsideration.

A further object if the invention is to provide an improved method oftreating magnesium alloys containing zirconium.

The alloy of the invention in its preferred form contains 6% of zinc andnot less than 0.7 nor more than 1 per cent of zirconium in magnesium. Inproducing such alloy it is rather difiicult to closely control theprecise proportions of minor components in the finished alloy. Inaccordance with the present invention, in no case should the zinc exceed7 per cent nor be less than 5 per cent. It is desirable that the zinccontent be not allowed to vary from the preferred 6 per cent by morethan 0.5 per cent. Less than 0.7 per cent of zirconium has been found togive markedly inferior results in the grain-size of the alloy and in theeffectiveness of the agein or heat treatment in developing maximumstrengthand ductility in the alloy.

It is believed by those skilled in the art of producingzirconium-containing magnesium alloys that it is zirconium, which is insolid solution, that eifects the grain size of the alloy. It is alsoknown that very careful foundry technique is essential to insure higheffective zirconium content in solid solution. When carefully preparedaccordingly the present alloy has an average grain diameter of 0.001 to0.002", in no case exceeding 0.003, and the following average mechanicalstrength properties:

Ultimate tensile strength, assoc-42,000 p. s. i. Yield strength,18,000-22,000 p. s. i. Elongation, 8 to 14% A comparison of this alloy,in the as cast condition, 1. e. without heat treatment, with similaralloys containing a smaller proportion of zinc shows that the presentalloy has much superior mechanical properties. This is illustrated by anincrease of as much as 13 per cent in ultimate tensile strength, 15 percent in yield strength and 2 Claims. (Cl. 148-21.90)

more than 30 per cent in elongation found in many test bars of thealloy.

A similar comparison of such alloys after hea treatment showed anincrease of as much as 30 per cent in ultimate tensile strength, 50 percent in yield strength and in elongation in bars tested.

An important characteristic of the alloy is that its mechanicalproperties of strength and hardness are developed by ageing at roomtemperature to a greater extent than in similar alloys.

It has been found that the effect of heat treatment on magnesium alloyscontaining zirconium,

with or without other metals, in the development of maximum desirablemechanical properties, i. e., strength and ductility, is much improvedby subjecting them to a homogenizing treatment at a high temperature andto an ageing treatment at a low temperature.

In accordance with the method of the invention, the cast alloys aresubjected to a homogenizing treatment at a temperature of at least 425C. for a short period which should not exceed five hours and to anageing treatment at a temperature not exceeding C. For the first stageof theheat treatment the preferred temperature is 475 to 500 C. andheating at such temperature for a period of one half hour is effective.A two hour period is preferred. At lower temperatures a somewhat longerperiod is preferred but this temperature should not be less than 425 C.In the second or ageing stage of the method the alloy is maintained at atemperature not exceed- 7 ing 150 C. for at least 24 hours, preferably48 hours.

To illustrate the effect of this treatment the following example isgiven:

An alloy containing magnesium and 5.88 per cent zinc and 0.82 per centzirconium in the as cast condition had an ultimate tensile strength of39,100 pounds per square inch, a yield strength of 20,800 p. s. i. andan elongation of 10.1 per cent. When this cast alloy was heattreated asabove described, the comparative figures were respectively 47,300,30,700 and 14.

What is claimed is:

1. A method of developing strength and ductility in magnesium castingalloys consistin essentially of magnesium, substantially 6% zinc and notless than 0.7 nor more than 1 zirconium which comprises subjecting thecast alloy to a homogenizing treatment at a temperature of 425 to 500 C.for a relatively short period of time not exceeding 5 hours butsufficient to eifect optimum homogeneity of the structure at theparticular temperature employed and thereafter to an ageing treatment ata. temperature not exceeding Number Name fiat 150 C. for at least 24hours and sufiicient to de- 2,224,151 Gauthier Dec. 10, 1940 velop inthe casting an ultimate tensile strength 2,286,311 Sauerwald June 16,1942 not less than 42,000 p. s. i., and a yield strength 2,314,853Brandt Mar. 23, 1943 substantially greaterxhan 25,30'0'pLs. i. 52,420,293 Beck et a1. 13, 1947 2. An alioy casting as and when producedby 2,520,753 Ball et a1." -"A*ug. '29, 1950 the method defined in claim1.

- Number Country Date REFERENCES CITED 7, 10 211,152 France Nov. 18,1940 The following references are of record in the OTHER REFERENCES meof this patent: se 3 69 749 s 1d t 1 (A P a) -r1a'o. ,L', auerwa ea.UNITED STATES PATENTS pfibfishedaune 15,1943 Number Name Date 15' "Deanet aL: Treatise in Transactions, Ameri- ,936,550 Gann et aL N0v. 21,1933 mnlnstitutezof Minin and Met, Engrs., vol. 171, 1,985,421 PaineDec. 25, I934 1947, pages'286-305;

1. A METHOD OF DEVELOPING STRENGTH AND DUCTILITY IN MAGNESIUM CASTINGALLOYS CONSISTING ESSENTIALLY OF MAGNESIUM, SUBSTANTIALLY 6% ZINC ANDNOT LESS THAN 0.7 NOR MORE THAN 1% ZIRCONIUM WHICH COMPRISES SUBJECTINGTHE CAST ALLOY TO A HOMOGENIZING TREATMENT AT A TEMPERATURE OF 425 TO500* C. FOR A RELATIVELY SHORT PERIOD OF TIME NOT EXCEEDING 5 HOURS BUTSUFFICIENT TO EFFECT OPTIMUM HOMOGENEITY OF THE STRUCTURE AT THEPARTICULAR TEMPERATURE EMPLOYED AND THEREAFTER TO AN AGEING TREATMENT ATA TEMPERATURE NOT EXCEEDING 150* C. FOR AT LEAST 24 HOURS AND SUFFICIENTTO DEVELOP IN THE CASTING AN ULTIMATE TENSILE STRENGTH NOT LESS THAN42,000 P.S.I., AND A YIELD STRENGTH SUBSTANTIALLY GREATER THAN 25,300P.S.I.